1. Field of the Invention
This invention relates to a method for the decomposition of a Michael type adduct of acrylic acid and/or an acrylic ester and more particularly to a method for the decomposition of a Michael type adduct, characterized by decomposing a Michael type adduct by-produced during the production of acrylic acid or an ester thereof by the action of heat or a catalyst, for example, in the presence of an N-oxyl compound into acrylic acid and/or an acrylic ester and/or at least one species of alcohol.
2. Description of the Related Art
Generally, during the production of acrylic acid and an ester thereof, a Michael type adduct having a carboxylic acid and an alcohol added to the carbon-carbon double bond of the acrylic acid and the acrylic ester is possibly by-produced by the action of heat or a catalyst, for example. Such Michael type adducts include about dimers to pentamers of acrylic acid, esters thereof, alkoxypropionic acids, and alkoxypropionic esters, for example.
When the quantity of the by-produced Michael type adduct increases, this increase brings the disadvantage of degrading the efficiency of raw materials in the process for the production of acrylic acid and an acrylic ester and boosting the cost of production. Further, when the Michael type adduct is suffered to accumulate in the process, it greatly hinders the step of purification and the step of production and, owing to the elevation of temperature and the formation of a by-product which ensues, possibly degrades the quality of a product. Thus, the Michael type adduct is generally concentrated at the step of purification, expelled from the process, and incinerated in the ambient air. This incineration is unfavorable from the viewpoint of the preservation of the environment. At the plant for the production of acrylic acid, therefore, efforts have been directed toward decomposing the Michael type adduct and reclaiming the products of the decomposition.
In regards to a method for decomposing such a Michael type adduct, it has been heretofore known that the oligomers of acrylic acid or an acrylic ester, alkoxypropionic acids, and alkoxypropionic esters are thermally decomposed or decomposed by the use of a catalyst. To be specific, JP-A-49-55614 discloses a method which consists in heating the Michael type adduct by-produced during the esterification of acrylic acid with an alcohol at a temperature of not lower than 180° C. thereby decomposing the adduct into monomers. Then, JP-B-45-19281 discloses a method which produces acrylic acid by heating the residue produced at the step for finishing acrylic acid in the presence of a catalyst such as a compound possessing a primary or tertiary amino group or a tertiary phosphine.
These methods, however, require fairly high temperatures and, in the meantime, suffer from unduly low recovery of acrylic acid. Further, an attempt to heighten the recovery in these methods results in promoting secondary reactions, copiously forming such by-products as high boiling substances and low boiling substances which degrade the quality of acrylic acid or an acrylic ester, and consequently rendering recovery of acrylic acid in high yields difficult.
Further, JP-A-03-178949 discloses a method for recovering monomers by catalytically decomposing the Michael type adduct by-produced during the production of acrylic acid and an ester thereof in the presence of a solid acid at an elevated temperature of not lower than 200° C. This method has a high decomposition of the Michael type adduct. Since the reaction of this method proceeds at a high temperature, however, it forms such by-products as light boiling substances at a high ratio and consequently brings an adverse effect on the quality of a product. Further, since the decomposition is a solid-liquid reaction, the catalytic activity is conspicuously degraded by poisoning. Moreover, since all the methods described above invariably resort to high-temperature reactions and consequently produce highly viscous residues, they are at a disadvantage in suffering the residues to solidify eventually after protracted stagnation and rendering the disposal of the solidified residues extremely difficult. Under these circumstances, the desirability of converting the Michael type adduct into at least one of such useful compounds as acrylic acid, esters thereof, and alcohols and efficiently recovering or utilizing the product of conversion has been finding enthusiastic recognition.